Error correction technology is essential technology for realizing highly reliable communication systems and information recording systems. Concatenated codes and iterated codes are codes that are formed from a combination of two types of codes (outer code and inner code). For instance, an RS code (Reed-Solomon code) or a BCH code (Bose-Chaudhuri-Hocquenghem code) is broadly used as the outer code, and a convolutional code, a turbo code or an LDPC code (Low Density Parity Check code) is broadly used as the inner code. In particular, the turbo code and the LDPC code are attracting attention as an error correction code for realizing performance that approaches the Shannon limit. The LDPC code and its decoding method are disclosed, for example, in Patent Document 1 (Japanese Patent Kokai 2006-279396).
Additionally, research on decoding algorithms having high error detection performance regarding the foregoing error correction codes is being conducted. Signals read from a recording medium such as an optical disk or an HD (hard disk) is not only susceptible to random errors, they are also susceptible to burst errors resulting from the damage of the recording medium or mechanical operation of the reproduction device. Decoding algorithms for detecting burst errors with high precision are disclosed, for example, in Patent Document 2 (Japanese Patent Kokai No. 2004-127408) and Patent Document 3 (Kokai No. 2005-166089). Nevertheless, since much time is required for the decoding processing if the error detection rate of the decoding algorithm becomes higher, there is a problem in that this may cause deterioration in the throughput.    Patent Document 1: Japanese Patent Kokai No. 2006-279396    Patent Document 2: Japanese Patent Kokai No. 2004-127408    Patent Document 3: Japanese Patent Kokai No. 2005-166089